A nuclear power plant using a pressurized-water reactor comprises a pressure vessel having a vertically substantially cylindrical side wall and containing the reactor core through which the pressurized-water coolant is circulated. The vessel's side wall has inlet and outlet coolant connections radiating from its upper portion, these outlet connections via pipes connecting with the heat exchangers of steam generators and from which pipes extend back via main coolant pumps to the vessel's inlet connections.
The pressure vessel is surrounded by a concrete wall formed by concrete defining a pit in which the vessel is positioned. The relative diameters of the two walls are such as to define an annular space between the two so as to accommodate instrumentation lowered into the pit for inspection of the pressure vessel's side wall condition.
In prior art installations this concrete wall has been designed to function not only as biological protection but also to contain missile-like fragments of the pressure vessel in the event its side wall ruptures under the pressure of the pressurized-water coolant circulating within the vessel. Therefore, the concrete construction has required expensive reinforcement, but because of the annular space, the concrete wall has been unable to function to reinforce the vessel's side wall against rupturing.
The coolant pipes extending to and from the steam generators also contain the pressurized-water coolant and the steam generators must operate under the internal pressure of the generated steam. These components are also surrounded by concrete walls, but in this instance the walls are spaced substantial distances from the components. This has made it possible to provide the steam generators and coolant pipes with rupture protection in the form of pressure-resistant and heat-resistant concrete segments which are interfitted to surround the components and which are themselves surrounded by high-tensile metal annular elements. In this way rupure protecting encasements are provided for these components, the encasement parts being relatively proportioned so that when the steam generators and coolant pipes are thermally expanded by their normal operating temperatures, the high-tensile metal annular elements, which remain cooler, resist the expansion, the result being that the high-compression strength segments are compressed against the walls of the steam generators and pipes to relieve them of a substantial amount of the stress resulting from their confinement of the high-pressure fluids. Such rupture protection for the steam generators and coolant pipes has been disclosed and claimed in the U.S. Michel et al. patent application Ser. No. 417,798, filed Nov. 21, 1973.
Now the previously described annular space between the reactor pressure vessel's side wall and its surrounding concrete wall must be small enough in radial extent to ensure containment of possibly flying fragments of the side wall in the event the latter should rupture under its internal pressure. Therefore, there is no room for working personnel and thus it has heretofore been impossible to encase the pressure vessel's side wall in the same manner as done in the case of the steam generators and coolant pipe lines. If the encasement were to be built on the vessel prior to its installation in its concrete pit, the encasement would fill up the annular space required to inspect the condition of the pressure vessel's side wall.